Just look:
http://www.glaceice.net/uploads/3/9/6/9/3969825/3969289_orig...
Because there's no air bubbles, the ice is perfectly clear. That's not a trivial fact. Humans innately like clear stuff! Just think how unappealing cloudy water is in comparison to clear water. The only exceptions arise from cases where we've learnt from experience that cloudiness is good (e.g. cloudy looking cider has more flavour)
What this means, is that without considering price, almost any person would rather use one of these ice cubes over a normal ice cube. So the potential market is measured in billions of people. Even if (for example) only 0.01% of the population would ever consider spending $325 for 50 ice cubes, that 0.01% is guaranteed to want these ice cubes.
It seems stupid, but it's actually brilliant. The weakness with this sort of model is that it's very easy for competitors to dominate the market. Gläce has established the demand and made ice sexy, but they have no hold on their customers. Someone could come in and sell a perfect ice maker for $200 and crush the pre-made high end ice market completely.